Gear shifting assembly for change-speed transmissions

ABSTRACT

A gear shifting assembly for change-speed transmissions of the type having several shifting members which are actuatable to thereby set the transmission to a desired speed position employs two fluid-operated motors the first of which can move a displacing member into register with a selected shifting member and the second of which thereupon actuates the selected shifting member by way of the displacing member. The admission of a pressurized fluid to and the evacuation of fluid from the cylinders of the motors is regulated by a system of valves which are operated by pressurized fluid or by an electronic control unit.

United States Patent Espenschied et al.

[ Feb. 26, 1974 GEAR SHIFTING ASSEMBLY FOR CHANGE-SPEED TRANSMISSIONS[75] Inventors: Helmut Espenschied, Ludwigsburg; Georg Rothfuss,Ditzingen; Joseph Sauer, Schwieberdingen, all of Germany [73] Assignee:Robert Bosch GmbH, Stuttgart,

Germany [22] Filed: May 8, 1972 [21] Appl. No.: 250,956

[30] Foreign Application Priority Data May l8, l97l Germany 2124624 [52]US. Cl. 74/335, 74/364 [5]] Int. Cl. Fl6h 5/06, Fl6h 3/08 [58] Field ofSearch... 74/335, 364, 753; 192/109 F [56] References Cited UNITEDSTATES PATENTS 3,489,100 l/l970 Hill 91/39] X Backus 74/335 PrimaryExaminer-Arthur T. McKeon Attorney, Agent, or Firm-Michael S. Striker 57 ABSTRACT A gear shifting assembly for change-speed transmissions ofthe type having several shifting members which are actuatable to therebyset the transmission to a desired speed position employs twofluid-operated motors the first of which can move a'displacing memberinto register with a selected shifting member and the second of whichthereupon actuates the selected shifting member by way of the displacingmember. The admission of a pressurized fluid to and the evacuation offluid from the cylinders of the motors is regulated by a system ofvalves which are operated by pressurized fluid or by an electroniccontrol unit.

37 Claims, 6 Drawing Figures PATENTEI] FEB26 I874 sum 2 or 6PAIENTEDFEBZSIBM SHEEI 5 0F 6 m mi 68 Ems Q: mm 5 G GEAR SHIFTINGASSEMBLY FOR CHANGE-SPEED TRANSMISSIONS BACKGROUND OF THE INVENTION Thepresent invention relates to improvements in change-speed transmissionsin general, and more particularly to improvements in means for changingthe speed positions of transmissions which are utilized in automotivevehicles or the like. Still more particularly, the invention relates toimprovements in so-called gearshift assisters or gear shiftingassemblies which can be used to select and thereupon engage a selectedspeed gear of a change-speed transmission.

One known mechanism discloses a hydraulically or pneumatically operatedgear shifting assembly for change-speed transmissions wherein a firstmotor serves to select a desired speed position and a second motorserves to engage the selected speed gear. The gear shifting assemblyfurther comprises a system of valves which regulate the admission andevacuation of fluid from the motors. The valves must be operated by handso that the assembly cannot be used in connection with automaticchange-speed transmissions.

SUMMARY OF THE INVENTION An object of the invention is to provide anovel and improved gear shifting assembly which can be used to selectthe speed positions of an automatic changespeed transmission,particularly a transmission for automotive vehicles.

Another object of the invention is to provide a gear shifting assemblywhich can be operated by remote control and which can be designed tocontrol the operation of change-speed transmissions with any desired orpractical number of different speed positions.

A further object of the invention is to provide the gear shiftingassembly with novel and improved fluidoperated motors for selection andactuation of gear shifting members in an automatic change-speedtransmission.

An additional object of the invention is to provide the gear shiftingassembly with a novel and improved system of valves which allow forautomatic selection and actuation of shifting members.

Still another object of the invention is to provide a gear shiftingassembly which, in the event of emergency, can be actuated by hand so asto allow for selection of desired speed positions even if the means forsupplying a pressurized hydraulic or pneumatic fluid happens to be outof commission of if one or more valves of the valve system whichcontrols the flow of fluid to and from the motors are defective or failto operate properly due to exhaustion or failure of the source ofelectrical energy.

The improved gear shifting assembly can be used to control achange-speed transmission of the type having a plurality of shiftingmembers which are actuatable to thereby set the transmission intodifferent speed positions. The gear shifting assembly comprises axiallyand- /or angularly movable displacing means (such as a coupling elementor a forked hub) which is movable into register with each shiftingmember of the transmission, a fluid-operated selector motor includingfirst cylinder means and first piston means movable in the firstcylinder means between a plurality of different angular or axialpositions to thereby effect a movement of the displacing means intoregister with selected shifting members, fluid-operated actuating motormeans having second cylinder means and second piston means movable withreference to the second cylinder means from a normal or neutral positionto at least one but preferably two operative positions to therebyactuate the selected shifting member by way of the displacing means, atleast one source of pressurized gaseous or liquid fluid, and automaticcontrol means preferably including an electronic control unit forremotecontrol operated valve means serving to regulate the flow of fluidwhich is furnished by the source or sources to and from the first andsecond cylinder means.

The first cylinder means may be provided with two fluid-admittingpressure ports located at the opposite sides of the first piston meansand with a plurality of fluid-discharging ports which are located in thepath of movement of the first piston means. The valve means thenincludes a directional control valve which is interposed between thesource of pressurized fluid and the pressure ports and is arranged toautomatically admit pressurized fluid to the pressure port at the higherpressure side of the first piston means. The valve means furtherincludes normally closed electromagnetic shutoff valves for thefluid-discharging ports whereby the first piston means automaticallymoves to a position in which it seals that discharging port which wasfree to permit an outflow of fluid from the first cylinder means inresponse to opening of the respective shutoff valve. As a result of itsmovement to such position, the first piston means causes the displacingmeans to move into register with a selected shifting member which isthereupon caused to perform an angular or translatory movement inresponse to movement of the second piston means from its neutralposition.

The first and second piston means are preferably movable in planes whichare at least substantially normal to each other, and each piston meansmay comprise at least one double-acting piston.

The valve means of the control means may comprise normally closed safetyvalve means interposed between the source of pressurized fluid and thetwo motors.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theimproved gear shifting assembly itself, however, both as to itsconstruction and its mode of operation, together with additionalfeatures and advantages thereof, will be best understood upon perusal ofthe following detailed description of certain specific embodiments withreference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagrammatic partlysectional view of a gear shifting assembly for change-speedtransmissions which embodies one form of the invention;

FIG. 2 is a similar view of a second gear shifting assembly;

FIG. 3 is a similar view of a third gear shifting assemy;

FIG. 4 is a similar view of a fourth gear shifting assembly;

FIG. 5 is a similar view of a fifth gear shifting assembly; and

FIG. 6 is a similar view of a sixth gear shifting assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1,there is shown a gear shifting assembly which comprises three maincomponents, namely, a source of pressurized fluid, a speed selecting orpreshifting motor with associated valves, and a shifting or actuatingmotor with associated valves. The assembly further comprises anelectronic control unit which produces shifting pulses for setting thechangespeed transmission to a selected speed position. The details ofthe electronic control unit form no part of the present invention.

The gear shifting assembly of FIG. 1 employs a source of pressurizedhydraulic fluid (e.g., oil) which includes a pump 1 driven by anelectric motor (not shown) and drawing fluid from a reservoir or tank 4.The pressure of fluid which is discharged by the pump 1 is limited by arelief valve 2 which opens a bypass to the reservoir 4 when the fluidpressure in a high pressure line 5 reaches a predetermined maximumpermissible value. The source of pressurized fluid further comprises asuitable accumulator 3 which is connected with the high pressure line 5and serves to compensate for eventual fluctuations in fluid pressure aswell as to constitute an auxiliary source of pressurized fluid.

The high pressure line 5 connects the outlet of the pump 1 and theaccumulator 3 with a fluid-operated speed selecting motor 7 through theintermediary of a specially designed directional control valve 13. Abranch 6 of the high pressure line 5 connects the accumulator 3 and theoutlet of the pump 1 with a fluidoperated shifting or actuating motor 8,again by way of a specially designed directional control valve 33similar to or identical with the valve 13.

The speed selecting motor 7 (hereinafter called selector motor forshort) comprises a hydraulic actuator cylinder for a double-actingreciprocable actuator piston 9 which is connected with an elongatedpiston rod 9. The latter extends beyond and is sealingly guided in bothends of the cylinder 10. Two pressure ports ll, 12 which are closelyadjacent to the respective ends of the cylinder 10 at the opposite sidesof the piston 9 are connected with the directional control valve 13 byway of conduits 11a, 12a and serve to admit pressurized fluid to therespective cylinder chambers 10a and 10b. The construction of thedirectional control valve 13 is such that it automatically connects thehigh pressure line 5 with that one of the cylinder chambers 10a, 10bwherein the pressure is or can be higher than in the other chamber. Adirectional control valve which can be utilized in the assembly of FIG.1 to control the flow of pressurized fluid from the high pressure lines5, 6 into the motors 7 and 8 is disclosed, for example, in the copendingapplication, Ser. No. 2l7,06l of Espenschied et al., Jan. 1 l, 1972. Anelectronic unit for the valves of the type shown in FIGS. 1 to 6 iscopending in the application, Ser. No. 162,339, filed on July 14, l97l.

The actuator cylinder 10 of the selector motor 7 is further providedwith four fluid-discharging return ports l4, l5, l6 and 17 which arerespectively controlled by normally closed electromagnetic shutoffvalves 18, 19, 20 and 21 and are located in the path of movement of thepiston 9 between the pressure ports ll, 12. The return ports 14-17 canadmit fluid into the reservoir 4 by way of a return line RL.

The right-hand end of the piston rod 9' extends well beyond therespective end of the cylinder 10 and is rotatable in the openings ofbores 22', 23', 24', 25' of four shifting members or fingers 22, 23, 24,25 which form part of a change-speed transmission for automotivevehicles. This end portion of the piston rod 9' is provided with atleast one but preferably more than one coupling or displacing element 26which can establish a torque-transmitting connection between the pistonrod 9 and a selected shifting member or finger when the displacingelement 26 is moved into the respective bore 22', 23, 24 or 25'. Suchaxial shifting of the element 26 takes place in response to movement ofthe actuator piston 9 toward the pressure port 11 or 12 of the cylinder10 in the selector motor 7. For example, the displacing element 26 maybe provided with one or more external splines which can entercomplementary grooves provided in the fingers 22, 23, 24 and 25 so thatthe respective finger is then compelled to share the angular movementsof the piston rod 9.

The rightmost portion of the piston rod 9 constitutes a splined shaft 27which can be rotated by a tilting box here shown as a one-armed lever28. The latter has internal grooves to receive the splines of the shaft27 so as to allow the piston rod 9 to move axially to the extent whichis necessary to move the displacing element 26 into register andtorque-transmitting engagement with the finger 22, 23, 24 or 25. Thelever 28 can be pivoted by a second piston rod 29' which forms part ofthe actuating motor 8. The piston rod 29 is normal to and crosses inspace with the piston rod 9' (see the true position of the piston rod 29as shown at TR in FIG. 1). The right-hand portion of FIG. I shows theaxis of the piston rod 29' in the plane of the drawing and the axis ofthe splined shaft 27 at right angles to such plane merely for the sakeof clarity.

Each of the fingers 22, 23, 24, 25 is articulately connected with ashifter fork (not shown) by one or more links L, and each shifter forkstraddles a sleeve or collar which can shift the corresponding speedgear of the change-speed transmission in an automotive vehicle.

The actuating motor 8 comprises an actuator cylinder 30 fordouble-acting reciprocable actuator piston 29 which is rigid with theaforementioned piston rod 29'. The piston rod 29 extends beyond and issealingly guided in both ends of the cylinder 30. The latter has twopressure ports 31, 32 which are connected with the directional controlvalve 33 by conduits 31a, 32a. Furthermore, the cylinder 30 is providedwith three fluid-discharging return ports 34, 35, 36 which arerespectively controlled by electromagnetic shutoff valves 37, 38, 39 andcan discharge fluid into the return line RL which can convey such fluidback into the reservoir 4.

That portion of the piston rod 29 which is adjacent to the lever 28 hasa recess or slot 40 for a suitably rounded (e.g., substantiallyspherical) end portion 28a of this lever so that the latter can bepivoted clockwise or counterclockwise, depending upon whether theactuator cylinder 30 receives pressurized fluid by way of the pressureport 31 or 32.

The left-hand end portion 9" of the piston rod 9', as viewed in FIG. 1,is of polygonal outline and is provided with a diametrically extendingopening or bore to facilitate the attachment of a wheel or analogousmanually operated means HW (indicated by broken lines) which allows formanually induced movements of the displacing element 26 in the event ofafailure of the hydraulic system. The wheel I-IW need not be permanentlymounted on the end portion 9"; it can be attached only in an emergency.A similar polygonal or facetted righthand end portion 29" of the pistonrod 29' can also receive a wheel or analogous manually operated movingmeans which can be manipulated to pivot the lever 28 and to thus turnthe piston rod 9. For example, each of the end portions 9", 29" can beprovided with one or more flats. A gear shifting assembly forchangespeed transmission is disclosed, for example, in US. Pat. No.3,522,867.

The Operation When the drive of the vehicle transmits to the electroniccontrol unit a signal to shift into another gear, the control unitautomatically initiates a series of operations including disengaging theclutch (not shown), disengaging the previously used speed gear,selecting the desired speed gear, electronic synchronization, engagingthe selected gear, and engaging the clutch.

The selection and engagement of the desired speed gear are carried outby the assembly of FIG. I as follows. The electronic control unitfurnishes a signal which opens one of the electromagnetic valves 18-21,for example, the shutoff valve 19. The valves 18-21 are normally closedso that the return ports 14-17 of the actuator cylinder 10 are sealedfrom the return line RL. When the shutoff valve 19 opens, the returnport is free to communicate with the reservoir 4 and the pressure in thecylinder chamber 10a decreases. This causes the directional controlvalve 13 to connect the high pressure line 5 with the right-hand chamber10b by way of the conduit 12a and pressure port 12 whereby the actuatorpiston 9 moves in a direction to the left, as viewed in FIG. 1, andcauses the displacing element 26 to enter the bore 23' of the shiftingmember or finger 23 when the piston 9 reaches and seals the return portIS. The axial movement of the piston 9 in a direction to the left isbraked by the rising fluid pressure in the cylinder chamber 10a so thatthe piston rod 9 is gradually decelerated while moving its displacingelement 26 into register with the finger 23. The piston 9 comes to restwhen it seals the return port 15 because the pressure in the chamber10!; then equals the pressure in the chamber 100. This causes the valvemember of the directional control valve 13 to assume a neutral positionin which the high pressure line 5 communicates with both chambers of thecylinder 10 to thereby insure that the piston 9 remains in the selectedposition of sealing engagement with the return port 15 in which thepiston rod 9' can transmit torque to the finger 23. This completes thespeed position selecting operation.

The electronic control unit thereupon transmits a signal to the shutoffvalve 37 or 39 so that the selected valve opens and connects therespective return port 34 or 36 with the return line RL. This causes thedirectional control valve 33 to admit pressurized fluid into thecylinder chamber 300 or 30b so that the piston rod 29' moves axially andpivots the lever 28 to thereby turn the piston rod 9 by way of thesplined shaft 27. The displacing element 26 actuates the finger 23 whichcauses the associated link L to move the corresponding fork with theresult that the desired speed position is set and the correspondingspeed gear is ready to drive the main or output shaft of thechange-speed transmission.

The double-acting piston 9 of the selector motor 7 is movable in a planewhich is at least substantially normal to the plane of movement of thedouble-acting piston in the actuating motor 8. The piston 29 is movablebetween the illustrated neutral position in which it seals the returnport 35 and two operative positions in which it respectively seals thereturn ports 34, 36. The neutral position is located between the twooperative positions. The piston 29 will move to its right-hand operativeposition if a selected link L is to move in a direction to the left, asviewed in FIG. 1. If a selected link L must be moved in a direction tothe right, the piston 29 is moved to its left-hand operative position.

An important advantage of the improved gear shifting assembly is thatits electromagnetic valves can be actuated by remote control so that thechanges in speed positions of the transmission including the shiftingmembers 22-25 can be brought about in automatic response to signalsfurnished by the electronic control unit. Such mode of operation is lesstiresome to the driver of the vehicle and the setting of transmission toa desired speed position takes up much less time than in thetransmission which is controlled by the aforementioned gear shiftingassembly utilizing a system of manually operated valves.

It was found that the improved gear shifting assembly can be used withparticular advantage to control change-speed transmissions having arelatively large number of speed positions, for example, six forwardspeeds and one reverse speed.

If the pressurized fluid is a gas, e.g., air, the ports 14-17 and 3436can discharge spent fluid to the atmosphere. Oil has been found to beparticularly suited for use as a pressurized medium in the gear shiftingassembly of the present invention.

The shifting members 22-25 (whose number may exceed or is less thanfour) normally serve to transmit motion to shifting sleeves or collarswhich, in turn, serve to shift speed gears in a change-speedtransmission. Such speed gears are normally in permanent mesh with thegears of a countershaft in the transmission. When the displacing element26 is moved by the piston rod 29' in response to movement of thedouble-acting piston 29 to one of its operative positions, the selectedspeed gear transmits torque to the output shaft of the transmission. Thetransmission of torque can take place by way of a suitable claw clutch.A sleeve or collar is normally designed in such a way that it canconnect either one of two speed gears with the output shaft of thetransmission and is straddled by the prongs of a fork which is shiftablelengthwise of a shaft or is rotatable by a coupling rod. In eachinstance, the forks are preferably grouped together so that they can bemoved by a control lever of the vehicle. Such control lever correspondsto the piston rod 9' which can select the desired speed position. Thecontrol lever is first moved to a neutral position and the selectedsleeve is thereupon shifted in the one or the other direction to therebymove the corresponding speed gear to its operative position.

Such construction of the improved gear shifting assembly that the pistonin the cylinder of the actuating motor moves in a plane which is normalto the plane of movements of piston in the actuating motor is desirablebecause of the presently preferred design of changespeed transmissionswherein the selection of a desired speed position takes place inresponse to movement of the selector means in a first direction and theactual engagement takes place in response to movement in a seconddirection which is normal to the first direction.

Those parts of the assembly shown in FIG. 2 which are identical with orclearly analogous to the corresponding parts of the assembly of FIG. 1are denoted by similar reference characters. The gear shifting assemblyof FIG. 2 also comprises a source of pressurized fluid which includesthe aforediscussed parts 1, 2, 3 and 4. The high pressure lines 5 and 6respectively serve to connect the outlet of the pump 1 with directionalcontrol valves 13 and 33 which are connected with the motors 7 and 8 inthe same way as described in connection with FIG. 1. The main differencebetween the assemblies of FIGS. 1 and 2 is that the second assemblyemploys different displacing means for transmitting motion from thepiston rod 9 of the actuator cylinder 10 to the shifting member orfinger 22", 23", 24" or 25". The right-hand portion of the piston rod 9(as viewed in FIG. 2) is provided with a longitudinally extendingtoothed rack 41 which meshes with a gear segment 42 provided on adisplacing hub or sleeve 42a which is rotatable and movable axially withthe piston rod 29 of the double-acting piston 29 in the actuatorcylinder 30. The displacing hub 42a is further provided with a fork 43which can be brought into register with a pallet on the finger 22", 23",24" or 25", depending on the angular position of the hub 42a (which is afunction of the axial position of the piston rod 9). The fingers 22"-25"can be pushed and/or pulled to transmit motion to links and shifterforks in the same way as described in connection with FIG. 1. Thesefingers receive translatory motion in response to axial movement of thepiston rod 29'. The piston 29 may but need not rotate with the pistonrod 29; all that counts is that the piston rod 29 shares all axialmovements of the piston 29 relative to the cylinder 30.

As an optional precautionary or safety measure, the assembly of FIG. 2further comprises two electromagnetic safety valves 57, 58 which arerespectively installed in the high pressure lines 5 and 6 upstream ofthe respective directional control valves 13 and 33. Each of thesesafety valves has a valve element movable betweentwo positions in one ofwhich it connects the high pressure line.5 or 6 with the respectivedirectional control valve 13 or 33 and in the other of which therespective high pressure line is connected with the reservoir 4.

The assembly of FIG. 2 further employs modified shutoff valve means forcontrolling the evacuation of fluid from the chamber a or 30b of theactuator cylinder 30 of the actuating motor 8. This valve meanscomprises three check valves 47, 48, 49 which respectively control theflow of fluid from the discharging ports 34, 35, 36 to the return lineRL and three normally deenergized electromagnetic pilot valves 44, 45,46 which respectively control the check valves 47, 48, 49. When thesolenoid of the pilot valve 44 is deenergized, the latter seals a branchconduit 34a which connects the discharging port 34 with the return lineRL by way of a conduit 34b. At the same time, the pilot valve 44connects the return line RL with a chamber 54 at the left-hand end of aplunger 53 in the body of the check valve 47. Such connection isestablished by way of a conduit 47a. A median portion of the plunger 53is sealingly guided in a portion 52 of the body of the check valve 47which is provided with an outlet 51 connecting the return line RL with achamber at the right-hand end of the plunger 53. A valve seat 47b in thebody of the check valve 47 is normally engaged by a spherical valveelement 56 which is biased against the seat 47b by a helical spring 560.This means that the outlet 51 is normally sealed from an outlet 50 whichis connected with the discharging port 34.

When the pilot valve 44 is energized, it connects the branch conduit 340with the chamber 54 by way of the conduit 47a and seals the conduit 34afrom the conduit 34b and hence from the return line RL. If thedoubleacting actuator piston 29 is thereupon moved in a direction to theleft, as viewed in FIG. 2, it expels fluid from the cylinder chamber 30aso that the pressure in the port 34, branch conduit 34a and chamber 54rises sufficiently to shift the plunger 53 in a direction to the rightso that the smaller-diameter cylindrical extension of this plunger movesthe spherical valve element 56 away from the seat 47b and allows fluidto flow from the discharge port 34, through the inlet 50, around thevalve element 56, through the seat 47b and outlet 51, and into thereturn line RL.

The construction of the check valves 48, 49 and pilot valves 45, 46 isrespectively identical with that of the just described valves 47 and 44.

The operation of the assembly of FIG. 2 is analogous to that of theassembly which is shown in FIG. 1. When the electronic control unitreceives a signal to effect a change in the speed position of thechange-speed transmission in the automotive vehicle, one of the shutoffvalves 18-21 is opened simultaneously with the safety valve 57 so thatthe high pressure line 5 can deliver pressurized fluid to thedirectional control valve 13. One of the discharge ports 14-17 connectsthe respective chamber 10a or 1012 of the actuator cylinder 10 with thereturn line RL. The piston rod 9 then moves axially so as to rotate thefork 43 of the displacing hub 42a on the piston rod 29 into registerwith one of the shifting members or fingers 2225. During such selectionof the speed position, double-acting piston 29 in the actuator cylinder30 dwells in the illustrated neutral position (this also holds true forthe piston 29 of FIG. 1). The piston 29 has been moved to such neutralposition in response to opening of the pilot valve 45 together with atleast one of the pilot valves 44, 46 so that the opening of the safetyvalve 58 in the high pressure line 6 resulted in a movement of thepiston 29 to the neutral position prior to a new speed selection.

The safety valves 57, 58 are opened by remote control prior to selectionof a new speed position. When the speed selection by way of the motor 7is completed, i.e., when the prongs of the fork 43 straddle the palleton the selected shifting member or finger 22", 23", 24" or 25", theelectronic control unit energizes one of the valves pilot 44, 46 tocause the piston rod 29' to move axially and to actuate the selectedfinger by way of the displacing hub 420 so as to engage the selectedspeed gear of the change-speed transmission. The solenoids of the safetyvalves 57, 58 are thereupon deenergized and the assembly is ready forthe next speed selecting and actuating operation.

The assembly of FIG. 3 employs a different shifting or actuating motor68. The motor 7 is identical with the similarly numbered motor of FIG.2.

The actuating motor 68 comprises a double-acting actuator piston 69having a piston rod 69 which is guided in and extends beyond both endsof the actuator cylinder 70. The piston 69 does not come into actualcontact with the cylinder 70 and its central portion constitutes alarger-diameter entraining collar 71 which is located exactly midwaybetween the axial ends of the piston. The central portion 72 of thecylinder 70 has a reduced internal diameter which is somewhat greaterthan the diameter of the collar 71. The axial length of the collar 71equals that of the central cylinder portion 72. Those smaller-diameterportions 69a, 69a of the actuator piston 69 which extend axially beyondthe collar 71 are surrounded by rings 73 each of which is in sealingengagement with the periphery of the respective smaller-diameter portion69a, 69a as well as with the internal surface of the cylinder 70 at thecorresponding side of the central portion 72. The collar 71 can move therings 73 axially of the cylinder 70 toward the respective stops 74 whichare shown in the form of internal shoulders of the cylinder 70. Thus,each ring 73 can move axially between an abutment which constitutes thecentral cylinder portion 72 and the respective stop 74. The axial lengthof each of the piston portions 69a, 69a equals the distance between astop 74 and the nearest axial end of the central cylinder portion orabutment 72.

The annular space which is surrounded by the abutment 72 communicateswith the return line RL by way of a fluid-discharging port 75. A firstpressure port 76 communicates with the cylinder 70 in the region to theleft of the left-hand stop 74, and a second pressure port 77communicates with the cylinder 70 in the region to the right of theright-hand stop 74. The flow of fluid into the ports 76, 77 iscontrolled by two check valves 80, 81 which, in turn, are controlled byelectromagnetic pilot valves 78, 79. The construction of the source ofpressurized fluid (including the parts 1-4 and the high pressure linesand 6) is the same as described in connection with FIG. 1.

The check valve 80 (which is identical with the other check valve 81)has an inlet 82 connected with the high pressure line 6 and an outlet 83which communicates with the pressure port 76 of the actuator cylinder 70and is normally sealed from the inlet 82 by a spherical valve element 90which is biased by a helical spring 90a so that it normally engages anannular seat 90b provided in the body of the check valve 80 between theinlet 82 and outlet 83. The check valve 80 has a second outlet 84 whichis connected with the return line RL. The spherical valve element 90 canbe moved away from the seat 90b by the cylindrical extension 91 of aplunger 86 which is reciprocably guided in the lefthand portion 85 ofthe body of the check valve 80.

The body of the check valve 80 is further provided with three axiallyspaced annular chambers 87, 88 and 89. The chamber 89 communicates withthe outlet 83, the chamber 88 communicates with the outlet 84, and thechamber 87 is connected with an outlet of the pilot valve 78. When thevalve element 90 engages its seat 90b, the chamber 89 is sealed from theinlet 82.

When the pilot valve 78 is energized in response to a signal from theelectronic control unit, it admits pressurized fluid into the chamber 87of the check valve 80 whereby such fluid exerts pressure against theleft-hand end face 87' of the plunger 86 with the result that theplunger moves in a direction to the right and its extension 91 moves thespherical valve element 90 off the seat 90b so that the spring 90astores additional energy. The extension 91 can engage and displace thevalve element 90 after the plunger 86 seals the second outlet 84 (andhence the chamber 88 and the return line RL) from the chamber 89. Thelatter is then connected with the inlet 82 so that the pressure port 76receives pressurized fluid from the high pressure line 6. Theenergization of pilot valve 78 must be preceded by energization of anelectromagnetic control valve 94 which can connect the high pressureline 6 with the pilot valves 78 and 79. Thus, in order that the plunger86 of the check valve may move the spherical valve element off the seat90b to thus connect the inlet 82 with the pressure port 76, the controlvalve 94 must be energized with the pilot valve 78 so that the lattercan admit pressurized fluid into the chamber 87. As mentioned above, thevalves 79 and 81 are respectively identical with the valves 78 and 80.

In order to effect a movement of the double-acting piston 69 in theactuating motor 68 from the illustrated neutral position, for example,in order to move the piston 69 in a direction to the right, as viewed inFIG. 3, the electromagnetic valves 94 and 78 are energized so that thechamber 87 of the check valve 80 receives pressurized fluid which actsagainst the end face 87' and moves the plunger 86 in a direction towardthe spherical valve element 90. During a first stage of its rightwardmovement, the plunger 86 seals the chamber 88 and second outlet 84 fromthe chamber 89. The opening of the valve element 90 follows so that thepressurized fluid can flow from the inlet 82 to the outlet 83 and thenceinto the pressure port 76 for entry into the left-hand chamber of theactuator cylinder 70. The piston 69 begins to move in a direction to theright and its collar 71 pushes the right-hand ring 73 toward and intoengagement with the righthand stop 74 in the cylinder 70. This causesthe piston rod 69 to move the displacing hub 42a and the previouslyselected shifting member or finger 22", 23", 24" or 25" so that thespeed ratio of the transmission is changed as a function of the axialposition of the piston rod 9 of the selector motor 7. When the piston 69is arrested as a result of engagement between the right-hand ring 73 andthe right-hand stop 74, the pressure in the outlet 83 of the check valve80 rises to match the pressure in the inlet 82 whereby the spring 90a isfree to expand and returns the spherical valve element 90 into sealingengagement with the seat 90b. The operation of the actuating motor 68 isanalogous when the piston 69 is to move in a direction to the left; theelectronic control unit then furnishes a signal which energizes thecontrol valve 94 and the pilot valve 79.

If the piston 69 of the actuating motor 68 is to be returned to itsneutral position, the electronic control unit furnishes a signal whichenergizes the control valve 94 simultaneously with the pilot valves 78argl 79. Thus, the pressure ports 76, 77 admit pressurized fluid intothe respective chambers of the cylinder 70. That ring 73 which engagesthe respective stop 74 is then caused to move toward the centralcylinder portion or abutment 72 and entrains the collar 71 so that thepiston 69 returns to the illustrated neutral position. When the piston69 reaches such neutral position, the pressure in the outlets 83 of thecheck valves 80 and 81 matches the pressure in the respective inlets 82so that the springs 90a of the check valves are free to return therespective spherical valve elements 90 to their sealing positions. Thiscompletes the operation which is to be carried out in order to returnthe piston 69 to its neutral position.

The assembly of FIG. 4 differs from the assembly of FIG. 3 in that itemploys a simplified actuating motor 108. The piston rod 109 extendsonly beyond one axial end of the actuator cylinder 110 and is connectedwith the displacing hub 42a as well as with a double-acting piston 109having a cylindrical extension 111 at that side which faces away fromthe piston rod 109'. The piston 109 is sealingly received in and isreciprocable relative to the left-hand portion of the cylinder 110.

, The extension 111 carries a ring 112 which is movable axially in alarger-diameter annular recess 113 of the cylinder 110. The internal andexternal surfaces of the ring 112 are respectively in sealing engagementwith the cylinder 110 and extension 111. The axial length of theextension 111 equals the axial length of the recess The check valves 80and 81 are respectively controlled by pilot valves 78, 79, and theassembly of FIG. 4 further comprises a control valve 94. The operationof this assembly is analogous to that of the assembly shown in FIG. 3.Thus, the piston rod 109 will move in a direction to the right inresponse to energization of the valves 78, 94, the piston rod 109' willmove in a direction to the left in response to energization of thevalves 79, 94, and the piston 109 will return to the illustrated neutralposition in response to simultaneous energization of the valves 94, 78and 79.

The selector motor 7 of the assembly shown in FIG. 5 is identical withthe motor 7 of FIG. 2, and the source of pressurized fluid in theassembly of FIG. 5 is identical with the source of FIG. 1. The actuatingmotor 118 of FIG. 5 has two discrete coaxial cylinders 120, 120' and atwin multistage actuator piston 119. The stages 123, 123 of the piston119 are respectively provided with and guided by piston rods 121, 121'which respectively extend through and beyond the left-hand andright-hand (outer) ends of the cylinders 120, 120'. Those (inner) endwalls of the cylinders 120, 120 which are nearer to each otherconstitute two stops 122, 122 for two rings 125, 125' which aresealingly guided and reciprocable in the cylinders 120, 120 and'respectively sealingly surround the stages 123, 123 of the piston 119.The stages 123, 123 are respectively provided with collars 124, 124'.The collars 124, 124 respectively serve to entrain the rings 125, 125'to the illustrated inner end positions when the piston 119 isrespectively caused to move in a direction to the right and to the left,as viewed in FIG. 5. Fluid-discharging ports 126, 126 of the cylinders120, 120 communicate with each other and with the return line Rl...These return ports are respectively adjacent to or provided in the endwalls or stops 122, 122'. The left-hand end of the cylinder 120communicates with a first pressure port 127, and the right-hand end ofthe cylinder 120= communicates with a second pressure port 128.

The valves 94, 78, 79 and 80, 81 are identical with the similarlyreferenced valves of FIG. 3. The operation of the assembly of FIG. 5 isanalogous to that of FIG. 3 or FIG. 4, i.e., the displacing hub 42a willmove in a direction to the right in response to opening of the valves 94and 78, the hub 42a will move in a direction to the left in response toopening of the valves 94, 79, and the piston 119 will reassume theillustrated neutral position in response to simultaneous opening of thevalves 94, 78 and 79. It will be noted that the hub 42a is mounteddirectly on the piston 119 intermediate the cylinders 120, 120. This hubcan rotate on but is movable axially with the piston 119. It is evident,however, that the hub 42a can be mounted on the piston rod 121 or 121'.

The assembly of FIG. 6 employs a select motor 7 which is identical withthe motor 7 of FIG. 2 and a modified actuating motor 138. The actuatorcylinder 141 of the motor 138 has a main piston 139 which is connectedwith a piston rod 140 serving to move the "displacirig hub lZiTThepiston 05140 extends only beyond one axial end of the cylinder 141. Themain piston 139 is in sealing engagement with the internal surface ofthe cylinder 141, and the right-hand portion of the cylinder 141accommodates an auxiliary piston 142 having a smaller-diameter extension143 partition 144 is provided with preferably axially parallel channels,bores 0r passages for thefluid.

A first fluid-admitting port 145 communicates with the cylinder 141immediately to the left of the partition 144 between the pistons 139,143, and a second port 146 can admit pressurized fluid at the left-handend of the cylinder 141, i.e., at the left-hand side of the main piston139. A third port 147 can admit fluid to the cylinder 141 in the regionlocated to the right of the auxiliary piston 142. The port 147 iscontrolled by a normally open check valve 149 which is controlled by anormally open electromagnetic pilot valve 148. The construction of thevalves 148, 149 is respectively identical to that of the valves 78, 80shown in FIG. 3. The pilot valve 148 must be energized in order to closethe checkvalve 149.

The port 145 is connected with an outlet of a second check valve 151which is normally closed and is con trolled by a normally deenergizedelectromagnetic pilot valve 150. The valves 150, 151 are respectivelyidentical with the valves 78, 80 of FIG. 3. The pilot valve 150 must beenergized in order to effect an opening of the check valve 151.

The inlets 149a, 151a of the check valves 149, 151 are respectivelycontrolled by spherical valve elements 149b, 15lb. These inletscommunicate with the port 146 of the cylinder 141 and with the outlet1536 of a check valve 153 which is identical with the check valve 80 ofFIG. 3 and is controlled by an electromagnetic pilot valve 152. Thepilot valve 152 is normally closed, i.e., it must be energized in orderto effect an opening of the check valve 153 so that the port 146 andinlets 149a, 151a then receive pressurized fluid from the outlet 153c.The inlet 153a of the check valve 153 is connected with the highpressure line 6 and this inlet can admit pressurized fluid to the outlet153C in response to energization of the pilot valve 152.

The operation of the assembly of FIG. 6 is as follows.

The angular position of the hub 42a is selected by the motor 7 in thesame way as described in connection with FIG. 2. As shown, the motor 7has caused the piston rod 9' to move the hub 42a to an angular positionin which the fork 43 is ready to move the shifting member or finger 23".

In order to move the piston rod 140 of the actuating motor 138 in adirection to the left, as viewed in FIG. 6, the electronic control unitfurnishes a signal which results in energization of the pilot valve 152simultaneously with energization of the pilot valve 150. The ports 145,146, 147 are then connected with the high pressure line 6. The sum ofpressures upon the auxiliary piston 142 is zero but the main piston 139moves in a direction to the left because the effective area of itsright-hand surface is larger than the effective area ofits left-handsurface.

If the main piston 139 is to move to its right-hand operative position,the pilot valves 152 and 148 are energized. The ports 145 and 147 arethen connected with the return line RL by way of the check valves 151and 149. The port 146 admits pressurized fluid into the cylinder chamberwhich is located to the left of the main piston 139 so that the lattermoves in a direction to the right.

The pilot valve 152 is energized alone if the main piston 139 is to bereturned to its neutral position. If the main piston 139 was located inits right-hand operative position, it is returned to the neutralposition by the auxiliary piston 142 and its extension 143. If the mainpiston 139 was located in its left-hand operative position, it isreturned to the neutral position by fluid which is admitted via port146. The main piston 139 reaches the neutral position when it abutsagainst the extension 143 while the auxiliary piston 142 abuts againstthe partition 144.

The improved gear shifting assembly is susceptible of many additionalmodifications. For example, the assembly of FIG. 1 can utilize one ofthe actuating motors which are shown in FIGS. 2-6. It is also within thepurview of the invention to replace the selector motor 7 and/or theactuating motor 8, 68, 108, 118 or 138 with a hydraulic or pneumaticmotor having a rotary (rather than reciprocable) piston. A rotary pistonmotor may comprise a rotary output shaft which carries a piston arrangedto turn in a concentric annular chamber of the cylinder. The admissionof pressurized fluid into and the evacuation of fluid from the cylinderof the rotary piston motor can be controlled by a system of valvessimilar to those described in connection with FIGS. 1 to 6. If theactuating motor 8 of FIG. 1 is replaced with a rotary piston motor, therotary output shaft of such motor can be directly coupled to the lever28 of FIG. 1. If the rotary piston motor replaces one of the actuatingmotors shown in FIGS. 2-6, the gear shifting assembly is provided withsuitable means for transforming the angular movement of the output shaftof such motor into an axial movement of the displacing hub 42a.Analogously, if the selector motor 7 is replaced with a rotary pistonmotor, the output shaft of such rotary piston motor can be directlycoupled with the displacing hub 42a.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featureswhich fairly constitute essential characteristics of the generic andspecific aspects of our contribution to the art and, therefore, suchadaptations should and are intended to be comprehended within themeaning and range of equivalence of the claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:

1. A gear shifting assembly for a change-speed transmission of the typehaving a plurality of shifting members actuatable to thereby set thetransmission into different speed positions, said assembly comprisingdisplacing means movable into register with each of said shiftingmembers; a fluidoperated selector motor including first cylinder meansand first piston means movable in said cylinder means between aplurality of positions to thereby effect a movement of said displacingmeans into register with selected shifting members, said cylinder meansbeing provided with two fluidadmitting pressure ports located at theopposite sides of said piston means and with a plurality offluiddischarging ports located in the path of movement of said pistonmeans; fluid-operated actuating motor means having second cylinder meansand second piston means movable from a neutral position to at least oneoperative position to thereby actuate the selected shifting member byway of said displacing means; a source of pressurized fluid; andautomatic control means including remote control operated valve meansfor regulating the flow of fluid which is furnished by said source toand from said cylinder means, said valve means including a directionalcontrol valve interposed between said pressure ports and said source andarranged to admit pressurized fluid to the pressure port at thehigher-pressure side of said first piston means, and normally closedelectromagnetic shutoff valves for said discharging ports whereby saidfirst piston means automatically moves to a position in which it sealsthat discharging port which was free to discharge fluid from said firstcylinder means in response to opening of the respective shutoff valve.

2. An assembly as defined in claim 1, wherein said first and secondpiston means are respectively movable in first and second planes whichare at least substantially normal to each other.

3. An assembly as defined in claim 2, wherein each of said piston meanscomprises at least one doubleacting piston and said second piston meansis movable between two operative positions, said neutral position beinglocated between said operative positions.

4. An assembly as defined in claim 1, wherein said valve means furthercomprises a normally closed solenoid operated safety valve interposedbetween said source and said directional control valve.

5. An assembly as defined in claim 1, wherein said first piston means isreciprocable between said positions and comprises rotary andreciprocable piston rod means extending beyond said first cylindermeans, said shifting members being rotatable about the axis of saidpiston rod means and having aligned openings therefor, said displacingmeans being provided on said piston rod means and being received in theopening of the selected shifting member in the corresponding position ofsaid first piston means whereby said displacing means can transmittorque to the selected shifting member, said second piston means beingarranged to rotate said piston rod means in response to movementrelative to said second cylinder means.

6. An assembly as defined in claim 5, wherein said second piston meanscomprises second piston rod means extending beyond and reciprocablerelative to said second cylinder means, and further comprising means forrotating the piston rod means of said first piston means in response tolengthwise movement of said second piston rod means.

7. An assembly as defined in claim 6, wherein said means for rotatingcomprises a lever rotatable with and movable axially of said firstmentioned piston rod means, said second piston rod means having a recessreceiving a portion of said lever to pivot the latter and to therebyturn said first mentioned piston rod means in response to axial movementof said second piston means relative to said second cylinder means.

8. An assembly as defined in claim 7, wherein said piston rod means arenormal to and cross in space with each other, said portion of said leverbeing of at least substantially spherical shape.

9. An assembly as defined in claim 7, wherein said first mentionedpiston rod means comprises a splined shaft which is movable axiallyrelative to and receives torque from said lever.

10. An assembly as defined in claim 1, wherein said displacing means isrotatable into register with selected shifting members in response toaxial movement of said first piston means relative to said firstcylinder means, said second piston means being arranged to move saiddisplacing means axially and to thereby actuate the selected shiftingmember in response to movement of said second piston means relative tosaid second cylinder means.

11. A gear shifting assembly for a change-speed transmission of the typehaving a plurality of shifting members actuatable to thereby set thetransmission into different speed positions, said assembly comprisingdisplacing means movable into register with each of said shiftingmembers; a fluid-operated selector motor including first cylinder meansand first piston means movable in said-cylinder means between aplurality of positions to thereby effect a movement of said displacingmeans into register with selected shifting members, said piston meanscomprising piston rod means having an elongated toothed rack and saiddisplacing means comprising a gear meshing with said rack, saiddisplacing means being rotatable into register with selected shiftingmembers in response to axial movement of said piston means relative tosaid cylinder means; fluidoperated actuating motor means having secondcylinder means and second piston means movable from a neutral positionto at least one operative position to thereby actuate the selectedshifting member by way of said displacing means, said second pistonmeans being arranged to move said displacing means axially and tothereby actuate the selected shifting member in response to movement ofsaid second piston means relative to said second cylinder means; asource of pressurized fluid; and automatic control means includingremote control operated valve means for regulating the flow of fluidwhich is furnished by said source to and from said cylinder means.

12. An assembly as defined in claim 11, wherein said second piston meansis movable axially relative to said second cylinder means and at rightangles to the axis of said first mentioned piston rod means, said gearbeing secured to said second piston rod means so that the latter rotatesin response to axial movement of said rack and moves axially with saidsecond piston means.

13. A gear shifting assembly for a change-speed transmission of the typehaving a plurality of shifting members actuatable to thereby set thetransmission into different speed positions, said assembly comprisingdisplacing means movable into register with each of said shiftingmembers; a fluid-operated selector motor including first cylinder meansand first piston means movable in said cylinder means between aplurality of positions to thereby effect a movement of said displacingmeans into register with selected shifting members; fluid-operatedactuating motor means having second cylinder means and second pistonmeans movable from a neutral position to at least one operative positionto thereby actuate the selected shifting member by way of saiddisplacing means, said second cylinder means comprising twofluid-admitting pressure ports at the opposite sides of said secondpiston means and a plurality of fluid-discharging ports located in thepath of movement of said second piston means; a source of pressurizedfluid; and automatic control means including remote control operatedvalve means for regulating the flow of fluid which is furnished by saidsource to and from said cylinder means, said valve means including adirectional control valve interposed between said pressure ports andsaid source and arranged to admit pressurized fluid to the pressure portat the higherpressure side of said second piston means, and normallyclosed shutoff valves for said discharging ports whereby said pistonmeans automatically moves to a position in which it seals thatdischarging port which is free to discharge fluid from said secondcylinder means in response to opening of the respective shutoff valve.

14. An assembly as defined in claim 13, wherein said second piston meansis movable between two operative positions located at the opposite sidesof said neutral position thereof, said discharging ports including afirst port which is sealed by said second piston means in said neutralposition thereof and two additional ports which are respectively sealedby said second piston means in the one and the other operative positionthereof.

15. An assembly as defined in claim 13, wherein said shutoff valves aresolenoid-operated valves.

16. An assembly as defined in claim 13, wherein each of said shutoffvalves comprises a normally closed check valve and a solenoid-operatedpilot valve which is energizable to thereby open the respective checkvalve.

17. An assembly as defined in claim 16, wherein each of said checkvalves comprises a substantially spherical valve element which normallydwells in a sealing position and a plunger which is movable axially inresponse to energization of the respective pilot valve to thereby movesaid valve element from said sealing position.

18. An assembly as defined in claim 17, wherein each of said checkvalves further comprises a body which defines a seat for said valveelement and includes a portion which guides said plunger for axialmovement, one end of said plunger being subjected to fluid pressure inresponse to energization of the respective pilot valve, said bodyfurther having an inlet in communication with the respective dischargingport and an outlet, said inlet and outlet being located at the oppositesides of said seat so as to be sealed from each other in the sealingposition of said valve element and each of said check valves furthercomprising means for biasing said valve element against the respectiveseat.

19. An assembly as defined in claim 13, wherein said valve means furthercomprises a normally closed solenoid-operated safety valve interposedbetween said source and said directional control valve.

20. A gear shifting assembly for a change-speed transmission of the typehaving a plurality of shifting members actuatable to thereby set thetransmission into different speed positions, said assembly comprisingdisplacing means movable into register with each of said shiftingmembers; a fluid-operated selector motor including first cylinder meansand first piston means movable in said cylinder means between aplurality of positions to thereby effect a movement of said displacingmeans into register with selected shifting members; fluid-operatedactuating motor means having second cylinder means and second pistonmeans movable from a neutral position to two operative positions tothereby actuate the selected shifting member by way of said displacingmeans, said second cylinder means comprising a substantially centrallylocated abutment, two stops located at the opposite sides of and axiallyspaced from said abutment, a pair of fluid-admitting pressure ports eachadjacent to one of said stops and a fluiddischarging port in the regionof said abutment, said second piston means comprising a centrallylocated collar having a diameter smaller than the internal diameter ofsaid abutment and a pair of smaller-diameter cylindrical portionsflanking said collar, said collar being in register with said abutmentin said neutral position of said second piston means and said actuatingmotor further comprising a pair of rings each surrounding and slidableon one of smaller-diameter portions, said collar being arranged tomaintain one of said rings in sealing engagement with one of saidpressure portsin one of said operative positions of said second pistonmeans and said collar being arranged to maintain the other of said ringsin sealing engagement with the other pressure port in the other of saidoperative positions of said second piston means; a source of pressurizedfluid; and automatic control means including remote control operatedvalve means for regulating the flow of fluid which is furnished by saidsource to and from said cylinder means.

21. An assembly as defined in claim 20, wherein said second piston meanscomprises a piston rod which extends beyond said second cylinder meansand rotatably supports said displacing means, said displacing meansbeing arranged to share the axial movements of said second piston means.

'22. An assembly as defined in claim 20, wherein the axial length ofsaid abutment equals the axial length of said collar and the distancebetween said abutment and either one of said stops equals the axiallength of one of said smaller-diameter portions, the axial length ofeach of said rings being less than said distance and said rings havingexternal surfaces in sealing engagement with the adjacent portions ofthe internal surface of said second cylinder means, said pressure portsbeing outwardly adjacent to the respective rings.

23. A gear shifting assembly for a change-speed transmission of the typehaving a plurality of shifting members actuatable to thereby set thetransmission into different speed positions, said assembly comprisingdisplacing means movable into register with each of said shiftingmembers, a fluid-operated selector motor including first cylinder meansand first piston means movable in said cylinder means between aplurality of positions to thereby effect a movement of said displacingmeans into register with selected shifting members; fluid-operatedactuating motor means having second cylinder means and second pistonmeans movable from a neutral position to first and second operativepositions to thereby actuate the selected shifting member by way of saiddisplacing means, said second piston means comprising a piston rodextending axially through and beyond one end of said second cylindermeans, a cylindrical extension extending g ward the other end of saidsecond cylinder means and a peripheral surface in sealing engagementwith the internal surface of said second cylinder means, said actuatingmotor means further comprising a ring sealingly surrounding saidextension and sealingly engaging the internal surface of an annularrecess of said second cylinder means, the axial length of said recessbeing equal to that of said extension and said second cylinder meanshaving a first fluid-admitting pressure port adjacent to said other endthereof, a second fluid-admitting pressure port adjacent to said one endthereof, and a fluid-discharging port adjacent to that axial end of saidrecess which is remote from said other end of said second cylindermeans, said second piston means being arranged to seal said dischargingport in said neutral position thereof and being movable from saidneutral position to said first and second operative positions thereof inresponse to admission of pressurized fluid by way of said first andsecond pressure port, respectively; a source of pressurized fluid; andautomatic control means including remote control operated valve meansfor regulating the flow of fluid which is furnished by said source toand from said cylinder means.

24. A gear shifting assembly for a change-speed transmission of the typehaving a plurality of shifting members actuatable to thereby set thetransmission into different speed positions, said assembly comprisingdisplacing means movable into register with each of said shiftingmembers; a fluid-operated selector motor including first cylinder meansand first piston means movable in said cylinder means between aplurality of positions to thereby effect a movement of said displacingmeans into register with selected shifting members; fluid-operatedactuating motor means having second cylinder means and second pistonmeans movable from a neutral position to at least one operative positionto thereby actuate the selected shifting member by way of saiddisplacing means, said second cylinder means comprising discrete coaxialfirst and second cylinders and said second piston means constituting atwin piston having first and second stages respectively reciprocable insaid first and second cylinders, each of said cylinders having an innerend nearer to and an outer end remote from the other cylinder and eachof said stages having a collar located in the respective cylinder andremote from the respective inner end, said actuating motor means furthercomprising first and second rings sealingly surrounding and slidable onsaid first and second stages between the respective collars and therespective inner ends, said rings having peripheral surfaces in sealingengagement with the internal surfaces of the respective cylinders andeach of said cylinders having a fluid-admitting pressure port adjacentto the respective outer end and a fluid-discharging port adjacent to therespective inner end; a source of pressurized fluid; and automaticcontrol means including remote control operated valve means forregulating the flow of fluid which is furnished by said source to andfrom said cylinder means.

25. An assembly as defined in claim 24, wherein said discharging portscommunicate with each other and said displacing means is rotatable onand axially movable with said second piston means intermediate saidfirst and second cylinders.

26. A gear shifting assembly for a change-speed transmission of the typehaving a plurality of shifting members actuatable to thereby set thetransmission into different speed positions, said assembly comprisingdisplacing means movable into register with each of said shiftingmembers; a fluid-operated selector motor including first cylinder meansand first piston means movable in said cylinder means between aplurality of positions to thereby effect a movement of said displacingmeans into register with selected shifting members; fluid-operatedactuating motor means having second cylinder means and second pistonmeans movable from a neutral position to at least one operative positionto thereby actuate the selected shifting member by way of saiddisplacing means, said second cylinder means comprising first and secondfluid-admitting pressure ports and said second piston means beingmovable be tween said neutral position and two operative positionswhereby one of said pressure ports admits pressurized fluid to move saidsecond piston means to one of said operative positions and the otherpressure port admits pressurized fluid to move said second piston meansto the other operative position; a source of pressurized fluid; andautomatic control means including remote control operated valve meansfor regulating the flow of fluid which is furnished by said source toand from said cylinder means, said valve means comprising normallyclosed first and second check valves respectively interposed betweensaid source and said first and second ports and normally closed discreteelectromagnetic pilot valves for said check valves.

27. An assembly as defined in claim 26, wherein each of said checkvalves comprises a body having an inlet for pressurized fluid, an outletconnected with the respective pressure port, a valve element normallyassuming a sealing position in which said inlet is sealed from saidoutlet, and a plunger movable axially in said body to thereby move saidvalve element from said sealing position, said plunger being arranged tomove axially in response to energization of the respective pilot valve.

28. An assembly as defined in claim 26, wherein said valve means furthercomprises normally closed electromagnetic control valve means interposedbetween said source and said check valves.

29. A gear shifting assembly for a change-speed transmission of the typehaving a plurality of shifting members actuatable to thereby set thetransmission into different speed positions, said assembly comprisingdisplacing means movable into register with each of said shiftingmembers; a fluid-operated selector motor including first cylinder meansand first piston means movable in said cylinder means between aplurality of positions to thereby effect a movement of said displacingmeans into register with selected shifting members; fluid-operatedactuating motor means having second cylinder means and second pistonmeans movable from a neutral position to at least one operative positionto thereby actuate the selected shifting member by way of saiddisplacing means, said second piston means comprising a main piston andan auxiliary piston both sealingly received in and reciprocable relativeto said second cylinder means, said auxiliary piston having asmaller-diameter extension extending toward said main piston and saidmain piston having a piston rod extending beyond one end of said secondcylinder means in a direction away from said auxiliary piston, saidactuating motor means further comprising a fluid-permeable partitionprovided in said second cylinder means to guide said extension and saidsecond cylinder means having a first fluid-admitting port located atthat side of said auxiliary piston which is remote from said mainpiston, a second fluid-admitting port located between said pistons, anda third fluid-admitting port adjacent to said one end of said secondcylinder means; a source of pressurized fluid; and automatic controlmeans including remote control operated valve means for regulating theflow of fluid which is furnished by said source to and from saidcylinder means.

30. An assembly as defined in claim 29, wherein said valve meanscomprises a first check valve for admitting pressurized fluid to saidfirst port, a normally deenergized first electromagnetic pilot valvewhich is energizable to thereby actuate said first check valve, a secondcheck valve interposed between said source and said second port,anormally deenergized second electromagnetic pilot valve which isenergizable to actuate said second check valve, a third check valveinterposed between said third port and said source, and a normallydeenergized third electromagnetic pilot valve which is energizable toactuate said third check valve.

31. An assembly as defined in claim 30, wherein said third check valveis arranged to control the admission of pressurized fluid from saidsource to said first and second check valves.

32. An assembly as defined in claim 31, wherein said first check valveis normally open and is arranged to close in response to energization ofsaid first pilot valve, said second and third check valves beingnormally closed and being arranged to respectively open in response toenergization of said second and third pilot valves.

33. A gear shifting assembly for a change-speed transmission of the typehaving a plurality of shifting members actuatable to thereby set thetransmission into different speed positions, said assembly comprisingdisplacing means movable into register with each of said shiftingmembers; a fluid-operated selector motor including first cylinder meansand first piston means movable in said cylinder means between aplurality of positions to thereby effect a movement of said displacingmeans into register with selected shifting members; fluid-operatedactuating motor means having second cylinder means and second pistonmeans movable from a neutral position to at least one operative positionto thereby actuate the selected shifting member by way of saiddisplacing means, said second cylinder means having at least onefluid-admitting pressure port; a source of pressurized fluid; andautomatic control means including remote control operated valve meansfor regulating the flow of fluid which is furnished by said source toand from said cylinder means, said valve means comprising a check valveinterposed between said source and said port and having a body providedwith a seat,

an inlet for pressurized fluid and an outlet connected with said port, avalve element movable into sealing engagement with said seat to therebyseal said inlet from said outlet, and a plunger movable in said bodyfrom an idle position to thereby move said valve element from saidsealing position, said body further having a chamber adjacent to thataxial end of said plunger which is remote from said valve element andsaid valve means further comprising pilot valve means actuatable toadmit pressurized fluid into said chamber to thereby effect a movementof said valve element from said sealing position.

34. An assembly as defined in claim 33, wherein said body of said checkvalve is further provided with a fluid-discharging second outlet whichcommunicates with said first mentioned outlet in the sealing position ofsaid valve element and is sealed from said first mentioned outlet bysaid plunger in response to admission of pressurized fluid into saidchamber, said check valve further comprising means for biasing saidvalve element to said sealing position.

35. An assembly as defined in claim 34, wherein said body is furtherprovided with a second chamber which communicates with said firstmentioned outlet and a third chamber which communicates with said secondoutlet, said chambers being spaced from each other as considered in theaxial direction of said plunger and said seat being provided betweensaid inlet and said second chamber.

36. An assembly as defined in claim 1, further comprising manuallyoperated means for moving at least one of said piston means in the eventof failure of said valve means.

37. An assembly as defined in claim 36, wherein said one piston means isprovided with a piston rod extending beyond the respective cylindermeans and said manually operated means is separably secured to saidpiston rod without the respective cylinder means.

1. A gear shifting assembly for a change-speed transmission of the typehaving a plurality of shifting members actuatable to thereby set thetransmission into different speed positions, said assembly comprisingdisplacing means movable into register with each of said shiftingmembers; a fluid-operated selector motor including first cylinder meansand first piston means movable in said cylinder means between aplurality of positions to thereby effect a movement of said displacingmeans into register with selected shifting members, said cylinder meansbeing provided with two fluid-admitting pressure ports located at theopposite sides of said piston means and with a plurality offluiddischarging ports located in the path of movement of said pistonmeans; fluid-operated actuating motor means having second cylinder meansand second piston means movable from a neutral position to at least oneoperative position to thereby actuate the selected shifting member byway of said displacing means; a source of pressurized fluid; andautomatic control means including remote control operated valve meansfor regulating the flow of fluid which is furnished by said source toand from said cylinder means, said valve means including a directionalcontrol valve interposed between said pressure ports and said source andarranged to admit pressurized fluid to the pressure port at thehigher-pressure side of said first piston means, and normally closedelectromagnetic shutoff valves for said discharging ports whereby saidfirst piston means automatically moves to a position in which it sealsthat discharging port which was free to discharge fluid from said firstcylinder means in response to opening of the respective shutoff valve.2. An assembly as defined in claim 1, wherein said first and secondpiston means are respectively movable in first and second planes whichare at least substantially normal to each other.
 3. An assembly asdefined in claim 2, wherein each of said piston means comprises at leastone double-acting piston and said second piston means is movable betweentwo operative positions, said neutral position being located betweensaid operative positions.
 4. An assembly as defined in claim 1, whereinsaid valve means further comprises a normally closed solenoid operatedsafety valve interposed between said source and said directional controlvalve.
 5. An assembly as defined in claim 1, wherein said first pistonmeans is reciprocable between said positions and comprises rotary andreciprocable piston rod means extending beyond said first cylindermeans, said shifting members being rotatable about the axis of saidpiston rod means and having aligned openings therefor, said displacingmeans being provided on said piston rod means and being received in theopening of the selected shifting member in the corresponding position ofsaid first piston means whereby said displacing means can transmittorque to the selected shifting member, said second piston means beingarranged to rotate said piston rod means in response to movementrelative to said second cylinder means.
 6. An assembly as defined inclaim 5, wherein said second piston means comprises second piston rodmeans extending beyond and reciprocable relative to said second cylindermeans, and further comprising means for rotating the piston rod means ofsaid first piston means in response to lengthwise movement of saidsecond piston rod means.
 7. An assembly as defined in claim 6, whereinsaid means for rotating comprises a lever rotatable with and movableaxially of said first mentioned piston rod means, said second piston rodmeans having a recess receiving a portion of said lever to pivot thelatter and to thereby turn said first mentioned piston rod means inresponse to axial movement of said second piston means relative to saidsecond cylinder means.
 8. An assembly as defined in claim 7, whereinsaid piston rod means are normal to and cross in space with each other,said portion of said lever being of at least substantially sphericalshape.
 9. An assembly as defined in claim 7, wherein said firstmentioned piston rod means comprises a splined shaft which is movableaxially relative to and receives torque from said lever.
 10. An asseMblyas defined in claim 1, wherein said displacing means is rotatable intoregister with selected shifting members in response to axial movement ofsaid first piston means relative to said first cylinder means, saidsecond piston means being arranged to move said displacing means axiallyand to thereby actuate the selected shifting member in response tomovement of said second piston means relative to said second cylindermeans.
 11. A gear shifting assembly for a change-speed transmission ofthe type having a plurality of shifting members actuatable to therebyset the transmission into different speed positions, said assemblycomprising displacing means movable into register with each of saidshifting members; a fluid-operated selector motor including firstcylinder means and first piston means movable in said cylinder meansbetween a plurality of positions to thereby effect a movement of saiddisplacing means into register with selected shifting members, saidpiston means comprising piston rod means having an elongated toothedrack and said displacing means comprising a gear meshing with said rack,said displacing means being rotatable into register with selectedshifting members in response to axial movement of said piston meansrelative to said cylinder means; fluid-operated actuating motor meanshaving second cylinder means and second piston means movable from aneutral position to at least one operative position to thereby actuatethe selected shifting member by way of said displacing means, saidsecond piston means being arranged to move said displacing means axiallyand to thereby actuate the selected shifting member in response tomovement of said second piston means relative to said second cylindermeans; a source of pressurized fluid; and automatic control meansincluding remote control operated valve means for regulating the flow offluid which is furnished by said source to and from said cylinder means.12. An assembly as defined in claim 11, wherein said second piston meansis movable axially relative to said second cylinder means and at rightangles to the axis of said first mentioned piston rod means, said gearbeing secured to said second piston rod means so that the latter rotatesin response to axial movement of said rack and moves axially with saidsecond piston means.
 13. A gear shifting assembly for a change-speedtransmission of the type having a plurality of shifting membersactuatable to thereby set the transmission into different speedpositions, said assembly comprising displacing means movable intoregister with each of said shifting members; a fluid-operated selectormotor including first cylinder means and first piston means movable insaid cylinder means between a plurality of positions to thereby effect amovement of said displacing means into register with selected shiftingmembers; fluid-operated actuating motor means having second cylindermeans and second piston means movable from a neutral position to atleast one operative position to thereby actuate the selected shiftingmember by way of said displacing means, said second cylinder meanscomprising two fluid-admitting pressure ports at the opposite sides ofsaid second piston means and a plurality of fluid-discharging portslocated in the path of movement of said second piston means; a source ofpressurized fluid; and automatic control means including remote controloperated valve means for regulating the flow of fluid which is furnishedby said source to and from said cylinder means, said valve meansincluding a directional control valve interposed between said pressureports and said source and arranged to admit pressurized fluid to thepressure port at the higher-pressure side of said second piston means,and normally closed shutoff valves for said discharging ports wherebysaid piston means automatically moves to a position in which it sealsthat discharging port which is free to discharge fluid from said secondcylinder means in response to opening of the respective shutoff valve.14. An assembly as defined in claim 13, wherein said second piston meansis movable between two operative positions located at the opposite sidesof said neutral position thereof, said discharging ports including afirst port which is sealed by said second piston means in said neutralposition thereof and two additional ports which are respectively sealedby said second piston means in the one and the other operative positionthereof.
 15. An assembly as defined in claim 13, wherein said shutoffvalves are solenoid-operated valves.
 16. An assembly as defined in claim13, wherein each of said shutoff valves comprises a normally closedcheck valve and a solenoid-operated pilot valve which is energizable tothereby open the respective check valve.
 17. An assembly as defined inclaim 16, wherein each of said check valves comprises a substantiallyspherical valve element which normally dwells in a sealing position anda plunger which is movable axially in response to energization of therespective pilot valve to thereby move said valve element from saidsealing position.
 18. An assembly as defined in claim 17, wherein eachof said check valves further comprises a body which defines a seat forsaid valve element and includes a portion which guides said plunger foraxial movement, one end of said plunger being subjected to fluidpressure in response to energization of the respective pilot valve, saidbody further having an inlet in communication with the respectivedischarging port and an outlet, said inlet and outlet being located atthe opposite sides of said seat so as to be sealed from each other inthe sealing position of said valve element and each of said check valvesfurther comprising means for biasing said valve element against therespective seat.
 19. An assembly as defined in claim 13, wherein saidvalve means further comprises a normally closed solenoid-operated safetyvalve interposed between said source and said directional control valve.20. A gear shifting assembly for a change-speed transmission of the typehaving a plurality of shifting members actuatable to thereby set thetransmission into different speed positions, said assembly comprisingdisplacing means movable into register with each of said shiftingmembers; a fluid-operated selector motor including first cylinder meansand first piston means movable in said cylinder means between aplurality of positions to thereby effect a movement of said displacingmeans into register with selected shifting members; fluid-operatedactuating motor means having second cylinder means and second pistonmeans movable from a neutral position to two operative positions tothereby actuate the selected shifting member by way of said displacingmeans, said second cylinder means comprising a substantially centrallylocated abutment, two stops located at the opposite sides of and axiallyspaced from said abutment, a pair of fluid-admitting pressure ports eachadjacent to one of said stops and a fluid-discharging port in the regionof said abutment, said second piston means comprising a centrallylocated collar having a diameter smaller than the internal diameter ofsaid abutment and a pair of smaller-diameter cylindrical portionsflanking said collar, said collar being in register with said abutmentin said neutral position of said second piston means and said actuatingmotor further comprising a pair of rings each surrounding and slidableon one of smaller-diameter portions, said collar being arranged tomaintain one of said rings in sealing engagement with one of saidpressure ports in one of said operative positions of said second pistonmeans and said collar being arranged to maintain the other of said ringsin sealing engagement with the other pressure port in the other of saidoperative positions of said second piston means; a source of pressurizedfluid; and automatic control means including remote control operatedvalve means for regulating the flow of fluid which is furnished by Saidsource to and from said cylinder means.
 21. An assembly as defined inclaim 20, wherein said second piston means comprises a piston rod whichextends beyond said second cylinder means and rotatably supports saiddisplacing means, said displacing means being arranged to share theaxial movements of said second piston means.
 22. An assembly as definedin claim 20, wherein the axial length of said abutment equals the axiallength of said collar and the distance between said abutment and eitherone of said stops equals the axial length of one of saidsmaller-diameter portions, the axial length of each of said rings beingless than said distance and said rings having external surfaces insealing engagement with the adjacent portions of the internal surface ofsaid second cylinder means, said pressure ports being outwardly adjacentto the respective rings.
 23. A gear shifting assembly for a change-speedtransmission of the type having a plurality of shifting membersactuatable to thereby set the transmission into different speedpositions, said assembly comprising displacing means movable intoregister with each of said shifting members, a fluid-operated selectormotor including first cylinder means and first piston means movable insaid cylinder means between a plurality of positions to thereby effect amovement of said displacing means into register with selected shiftingmembers; fluid-operated actuating motor means having second cylindermeans and second piston means movable from a neutral position to firstand second operative positions to thereby actuate the selected shiftingmember by way of said displacing means, said second piston meanscomprising a piston rod extending axially through and beyond one end ofsaid second cylinder means, a cylindrical extension extending toward theother end of said second cylinder means and a peripheral surface insealing engagement with the internal surface of said second cylindermeans, said actuating motor means further comprising a ring sealinglysurrounding said extension and sealingly engaging the internal surfaceof an annular recess of said second cylinder means, the axial length ofsaid recess being equal to that of said extension and said secondcylinder means having a first fluid-admitting pressure port adjacent tosaid other end thereof, a second fluid-admitting pressure port adjacentto said one end thereof, and a fluid-discharging port adjacent to thataxial end of said recess which is remote from said other end of saidsecond cylinder means, said second piston means being arranged to sealsaid discharging port in said neutral position thereof and being movablefrom said neutral position to said first and second operative positionsthereof in response to admission of pressurized fluid by way of saidfirst and second pressure port, respectively; a source of pressurizedfluid; and automatic control means including remote control operatedvalve means for regulating the flow of fluid which is furnished by saidsource to and from said cylinder means.
 24. A gear shifting assembly fora change-speed transmission of the type having a plurality of shiftingmembers actuatable to thereby set the transmission into different speedpositions, said assembly comprising displacing means movable intoregister with each of said shifting members; a fluid-operated selectormotor including first cylinder means and first piston means movable insaid cylinder means between a plurality of positions to thereby effect amovement of said displacing means into register with selected shiftingmembers; fluid-operated actuating motor means having second cylindermeans and second piston means movable from a neutral position to atleast one operative position to thereby actuate the selected shiftingmember by way of said displacing means, said second cylinder meanscomprising discrete coaxial first and second cylinders and said secondpiston means constituting a twin piston having first and second stagesrespectively reciprocable in said first and second cylinders, each ofsaid cylinders having an inner end nearer to and an outer end remotefrom the other cylinder and each of said stages having a collar locatedin the respective cylinder and remote from the respective inner end,said actuating motor means further comprising first and second ringssealingly surrounding and slidable on said first and second stagesbetween the respective collars and the respective inner ends, said ringshaving peripheral surfaces in sealing engagement with the internalsurfaces of the respective cylinders and each of said cylinders having afluid-admitting pressure port adjacent to the respective outer end and afluid-discharging port adjacent to the respective inner end; a source ofpressurized fluid; and automatic control means including remote controloperated valve means for regulating the flow of fluid which is furnishedby said source to and from said cylinder means.
 25. An assembly asdefined in claim 24, wherein said discharging ports communicate witheach other and said displacing means is rotatable on and axially movablewith said second piston means intermediate said first and secondcylinders.
 26. A gear shifting assembly for a change-speed transmissionof the type having a plurality of shifting members actuatable to therebyset the transmission into different speed positions, said assemblycomprising displacing means movable into register with each of saidshifting members; a fluid-operated selector motor including firstcylinder means and first piston means movable in said cylinder meansbetween a plurality of positions to thereby effect a movement of saiddisplacing means into register with selected shifting members;fluid-operated actuating motor means having second cylinder means andsecond piston means movable from a neutral position to at least oneoperative position to thereby actuate the selected shifting member byway of said displacing means, said second cylinder means comprisingfirst and second fluid-admitting pressure ports and said second pistonmeans being movable between said neutral position and two operativepositions whereby one of said pressure ports admits pressurized fluid tomove said second piston means to one of said operative positions and theother pressure port admits pressurized fluid to move said second pistonmeans to the other operative position; a source of pressurized fluid;and automatic control means including remote control operated valvemeans for regulating the flow of fluid which is furnished by said sourceto and from said cylinder means, said valve means comprising normallyclosed first and second check valves respectively interposed betweensaid source and said first and second ports and normally closed discreteelectromagnetic pilot valves for said check valves.
 27. An assembly asdefined in claim 26, wherein each of said check valves comprises a bodyhaving an inlet for pressurized fluid, an outlet connected with therespective pressure port, a valve element normally assuming a sealingposition in which said inlet is sealed from said outlet, and a plungermovable axially in said body to thereby move said valve element fromsaid sealing position, said plunger being arranged to move axially inresponse to energization of the respective pilot valve.
 28. An assemblyas defined in claim 26, wherein said valve means further comprisesnormally closed electromagnetic control valve means interposed betweensaid source and said check valves.
 29. A gear shifting assembly for achange-speed transmission of the type having a plurality of shiftingmembers actuatable to thereby set the transmission into different speedpositions, said assembly comprising displacing means movable intoregister with each of said shifting members; a fluid-operated selectormotor including first cylinder means and first piston means movable insaid cylinder means between a plurality of positions to thereby effect amovement of said displacing means into register with selected shiftiNgmembers; fluid-operated actuating motor means having second cylindermeans and second piston means movable from a neutral position to atleast one operative position to thereby actuate the selected shiftingmember by way of said displacing means, said second piston meanscomprising a main piston and an auxiliary piston both sealingly receivedin and reciprocable relative to said second cylinder means, saidauxiliary piston having a smaller-diameter extension extending towardsaid main piston and said main piston having a piston rod extendingbeyond one end of said second cylinder means in a direction away fromsaid auxiliary piston, said actuating motor means further comprising afluid-permeable partition provided in said second cylinder means toguide said extension and said second cylinder means having a firstfluid-admitting port located at that side of said auxiliary piston whichis remote from said main piston, a second fluid-admitting port locatedbetween said pistons, and a third fluid-admitting port adjacent to saidone end of said second cylinder means; a source of pressurized fluid;and automatic control means including remote control operated valvemeans for regulating the flow of fluid which is furnished by said sourceto and from said cylinder means.
 30. An assembly as defined in claim 29,wherein said valve means comprises a first check valve for admittingpressurized fluid to said first port, a normally deenergized firstelectromagnetic pilot valve which is energizable to thereby actuate saidfirst check valve, a second check valve interposed between said sourceand said second port, a normally deenergized second electromagneticpilot valve which is energizable to actuate said second check valve, athird check valve interposed between said third port and said source,and a normally deenergized third electromagnetic pilot valve which isenergizable to actuate said third check valve.
 31. An assembly asdefined in claim 30, wherein said third check valve is arranged tocontrol the admission of pressurized fluid from said source to saidfirst and second check valves.
 32. An assembly as defined in claim 31,wherein said first check valve is normally open and is arranged to closein response to energization of said first pilot valve, said second andthird check valves being normally closed and being arranged torespectively open in response to energization of said second and thirdpilot valves.
 33. A gear shifting assembly for a change-speedtransmission of the type having a plurality of shifting membersactuatable to thereby set the transmission into different speedpositions, said assembly comprising displacing means movable intoregister with each of said shifting members; a fluid-operated selectormotor including first cylinder means and first piston means movable insaid cylinder means between a plurality of positions to thereby effect amovement of said displacing means into register with selected shiftingmembers; fluid-operated actuating motor means having second cylindermeans and second piston means movable from a neutral position to atleast one operative position to thereby actuate the selected shiftingmember by way of said displacing means, said second cylinder meanshaving at least one fluid-admitting pressure port; a source ofpressurized fluid; and automatic control means including remote controloperated valve means for regulating the flow of fluid which is furnishedby said source to and from said cylinder means, said valve meanscomprising a check valve interposed between said source and said portand having a body provided with a seat, an inlet for pressurized fluidand an outlet connected with said port, a valve element movable intosealing engagement with said seat to thereby seal said inlet from saidoutlet, and a plunger movable in said body from an idle position tothereby move said valve element from said sealing position, said bodyfurther having a chamber adjacent to that axial end of said plungerwhich is remote from said valve element and said valve means furthercomprising pilot valve means actuatable to admit pressurized fluid intosaid chamber to thereby effect a movement of said valve element fromsaid sealing position.
 34. An assembly as defined in claim 33, whereinsaid body of said check valve is further provided with afluid-discharging second outlet which communicates with said firstmentioned outlet in the sealing position of said valve element and issealed from said first mentioned outlet by said plunger in response toadmission of pressurized fluid into said chamber, said check valvefurther comprising means for biasing said valve element to said sealingposition.
 35. An assembly as defined in claim 34, wherein said body isfurther provided with a second chamber which communicates with saidfirst mentioned outlet and a third chamber which communicates with saidsecond outlet, said chambers being spaced from each other as consideredin the axial direction of said plunger and said seat being providedbetween said inlet and said second chamber.
 36. An assembly as definedin claim 1, further comprising manually operated means for moving atleast one of said piston means in the event of failure of said valvemeans.
 37. An assembly as defined in claim 36, wherein said one pistonmeans is provided with a piston rod extending beyond the respectivecylinder means and said manually operated means is separably secured tosaid piston rod without the respective cylinder means.